Guest Posted September 15, 2005 Report Share Posted September 15, 2005 hi. i downloaded some freeware programs at this site, like the oscilloscope connected in the sound card. what are the probes that can be used to do your measurements? Quote Link to comment Share on other sites More sharing options...
autir Posted September 16, 2005 Report Share Posted September 16, 2005 HiI use a stereo jack to rca cableand then I connect the signal to the rca's signal (pin) and ground to the rca's ground (the round metal rim).It is the simplest, cheapest and most crude way to use an audio card oscilloscope. The fidelity of the signal will be mediocre due to losses caused by the connections and the cables. Not to mention that if you apply excessive voltage you may destroy your sound card (or more...).The proper way is to build a circuit like this. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 16, 2005 Report Share Posted September 16, 2005 That's a good interface circuit to protect the sound card from damage, except its output voltage swing of up to 11V positive or negative might still cause damage. Check the absolute max input voltage spec for your sound card. The circuit will also work fine with a positive 5V and negative 5V supply.The TL082 dual opamp is noisy. A TL072 is a low-noise version and costs less.The TL082 and TL072 dual opamps oscillate at a very high frequency when they directly drive the capacitance of a shielded cable. Therefore I recommend adding a 100 ohm resistor to the circuit's output (the pot's slider) in series with the shielded output cable. ;D Quote Link to comment Share on other sites More sharing options...
autir Posted October 15, 2005 Report Share Posted October 15, 2005 Anybody cares to explain how does the "150V input protection" part work?I am thinking of building a similar circuit for my computer. I don't care about output amplification and adjustment, I just want to increase the input impedance and protect my computer's soundcard from burning. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 16, 2005 Report Share Posted October 16, 2005 Anybody cares to explain how does the "150V input protection" part work?The article explains pretty well how it works.D1 or D2 conduct if the input voltage exceeds the power supply voltage by a forward diode voltage drop (0.6V) and clamp the voltage at the output from exceeding +12.6V and -12V.R2 limits the current when the input voltage is too high. The 1/2W rating for R2 occurs when the input voltage is 150V.C3 couples high frequencies around R2 so that they are not attenuated by the lowpass filter caused by R2 and the capacitance to ground at its output. ;D Quote Link to comment Share on other sites More sharing options...
autir Posted October 16, 2005 Report Share Posted October 16, 2005 Thanks. :D Quote Link to comment Share on other sites More sharing options...
TestGuru Posted October 26, 2006 Report Share Posted October 26, 2006 The sound card oscilloscope probe is available at: www.virtins.com Quote Link to comment Share on other sites More sharing options...
mugsby Posted October 27, 2006 Report Share Posted October 27, 2006 use a ganged pot to make a voltage divider, zeners as clamps and remove the cap from the soundcard and make it switchable, you might want to add a small bypass cap on the input as a precaution with hf's and a coupling transformer so you can test with ground mismatches. Quote Link to comment Share on other sites More sharing options...
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